FIG. 9 is a perspective outline view showing a general construction of a prior art electronic game system. By way of example, FIG. 9 shows an electronic game system using an electronic game machine manufactured by the present applicant's assignee (Super Nintendo Entertainment System). In FIG. 9, a non-volatile memory cartridge 2, in which the software necessary for running the game is stored, is detachably connected to a main console 1. At the front side of the main console 1, connectors for controllers (hereinafter "connectors") 11a, 11b are provided, and controllers 3 are connected to these connectors. The controllers 3 provide data and control signals to the main console 1 which together form an electronic game machine. A television receiver (hereinafter "television") 4 is also connected to the main console to display the game video frame.
FIG. 10 is a block diagram showing the constitution of the electronic game machine shown in FIG. 9, especially the detail of the connections between the controllers and the main body apparatus. In FIG. 10, inside the main body apparatus 1 are provided a main memory CPU 12, an internal circuit 13, an input/output IC (hereinafter "I/O") 14. The memory cartridge 2 is connected to the main CPU 12 through a cartridge connector. The main CPU 12 sends a write signal WE, a read signal RE, an address signal AD, and a data signal D1 to the I/O 14. The I/O 14 has as many ports as the number of connectors (two ports, A and B in the illustrated example), and each port is connected to each controller 3 through a corresponding connector. From each port of the I/O 14 to the controllers, a reset signal RST and a clock signal CL are given. From the controllers 3 to the corresponding ports, a data signal D2 is given. Reference numeral L1 is a power source line and L2 is a grounding line.
In the prior art electronic game machine, as described above, the I/O 14 must be provided with at least as many ports as the number of connectors. Hence the number of pins provided in the I/O 14 increases and the price of the IC chip comprising the I/O 14 is raised. Besides, in order to extend the number of connectors to be connected to the main body apparatus I in the future, either the I/O 14 must be preliminarily provided with extra ports in consideration of the future extension in the number of connectors, or it must be replaced with an I/O having more ports at the time of the extension. In either case, the provisions required to ensure that the I/O chip can accommodate future expansion was poor.
In the prior art electronic game machine, in order to exchange signals between the I/O 14 and controllers 3, at least three signal lines are needed (a signal line for reset signal RST, a signal line for clock signal CL, and a signal line for data signal D2). This then requires many pins on the I/O 14.
It is hence a primary object of the invention to present an electronic game machine that will better accommodate future expansion, and that will do so in a simple way with a main body apparatus and controllers to be used therein.